The invention relates generally to water pumps and more specifically to a temperature controlled variable speed water pump.
Today, most automobiles have an engine driven water pump wherein the flow characteristic of the pump is directly proportional to the speed of a water pump pulley which is typically driven at a ratio to the engine crank pulley via a belt. The ratio of the drive pulley, pump speed range, engine heat output, and radiator efficiency are among the numerous factors that contribute to the overall design of the water pump.
One approach currently used to provide more precise control of cooling capabilities of fan drives is to utilize a viscous fan clutch to drive the fan. Typically, these viscous fan clutches use a bimetallic control member in combination with a valve arm to control the amount of fluid entering the working chamber through the fill hole to the clutch working chamber. The bimetallic control member is typically affixed to the outside of the output member and reacts to underhood air temperature (indirect of engine temperature) to either open or close the fill hole.
A similar approach may be extremely beneficial for use in controlling a water pump. It is thus highly desirable to provide a water pump having a bimetallic controlled viscous clutch integral to the pump impeller. This solution is desirable to decrease the complexity of the overall design compared to an electrically controlled or fully electric water pump.
The above objects are accomplished by introducing a controllable viscous clutch that is integral to a water pump. The pump impeller is part of the output member of the clutch while the input is composed of a central drive shaft (attached to a pulley) and a clutch plate. As with a viscous fan clutch, the output member consists of two halves, a cover and a body. These components are made of a thermally conductive material constructed to provide sufficient heat transfer for the slipping clutch.
The viscous clutch is controlled similar to a viscous fan drive having a bimetallic control element wherein the viscous fluid flows from a reservoir chamber through a fill hole and into the working chamber defined between the output member and input member, where torque is transferred from the input to the output through fluid shear forces created within the working chamber. The fluid is returned to the reservoir by way of a differential speed (scavenge) pump.
The present invention locates this bimetallic control element internally within the output member of the device that, because of the location of the clutch, is a function only of the engine coolant temperature and not ambient air temperature.
The present invention delivers low coolant flow during cold engine conditions and higher, speed-limited flow once the engine exceeds a predetermined temperature. This will allow for faster engine warm-up resulting in improved occupant comfort, decreased tailpipe emissions, increased fuel economy, added safety due to faster defroster warm up, and increased water pump and cooling system life due to eliminating pump cavitation.
Other features, benefits and advantages of the present invention will become apparent from the following description of the invention, when viewed in accordance with the attached drawings and appended claims.